1. Field of the Invention
The cable connection method is a method of connecting to conductors within a triaxial electrical cable, without completely severing the cable, allowing compact, low cost connections to be made while having the added benefit of strain relief of the cable around the connection point and even within the cable itself.
2. Description of the Prior Art
Coaxial cables have been in use for many years. A common problem is connecting to a coaxial cable to access the signal on the inner conductor of the cable without completely severing the cable. Many inventions have been created to aid the goal of connecting to coaxial cables, typically by puncturing or removing part of the outer shield and insulation to access the inner conductor. These will be reviewed, and their applicability in connecting to triaxial cables evaluated.
For the purposes of reference, a triaxial cable is considered to have a first center conductor, an inner tubular shield conductor situated around the first center conductor and separated from it by a dielectric material (with optional semi-conductive outer layer for handling-noise suppression), an outer tubular shield conductor situated around the inner shield conductor and separated from it by an additional dielectric material, and an overall insulating layer.
Edlen, et al. (U.S. Pat. No. 2,694,182, Nov. 9, 1954) discloses a coaxial cable tap that pierces the outer insulator, shield and inner insulator to contact the center conductor using a hinged clamp assembly. Peripheral probes contact the shield to connect it electrically to other coaxial cables. While this performs suitably with coaxial cables, triaxial cables have and additional conducting layer that would require impractical piercing parts to connect to each conductor, such piercing parts being specially insulated and demanding critical positioning.
A functionally similar method is disclosed in Rheinfelder (U.S. Pat. No. 3,543,222, Nov. 24, 1970), and consists of a coaxial cable tap that pierces the outer insulator, shield and inner insulator to contact the center conductor and route its signal to one or more other coaxial cables. For triaxial cable connection, this is impractical, as cited for Edlen, above.
Rheinfelder (U.S. Pat. No. 3,625,623, Dec. 7, 1971) describes a method of accessing the conductors in a coaxial cable using a boring tool situated radially with respect to the central axis of the cable. Such a boring method adequately exposes the center conductor in a coaxial cable, but would not adequately also expose the inner shield conductor in a triaxial cable such that it could be easily connected to.
Down, et al. (U.S. Pat. No. 4,738,009, Apr. 19, 1988) discloses a coaxial cable tap that removes a semicircular section of the cable, then connects to the shield and center conductor using a clamping shell assembly. This method and assembly results in a coaxial cable tap construct that appears from the drawings to be approximately 10 to 15 times the cable diameter in length, which is unacceptably large. However, removal of a semicircular section of a triaxial cable would allow access to all three conductors and connection thereto.
The prior art is concerned with making connections to coaxial cables as are typically used in cable television distribution and radio frequency systems, where the connections must be made without interrupting service to customers, and where the impedance of the completed connection must not disturb the signals or system. In the case of a connection being made during factory assembly of a product, interruption of service is not an issue, and simpler methods may be used. With audio cables and systems, the characteristic impedance of the cable and connections is not important. While the prior art regarding coaxial cable taps provides some direction, it does not provide a solution that affords compact, low cost, strain relieved connections to audio triaxial cable.
After an electrical connection is made to a cable, it is also important to stabilize the connection against physical damage and encroaching moisture and contaminants. This is typically done with a sealing gasket or potting (encapsulating) operations. Of interest here are strain reliefs formed using epoxy or other potting compounds, as opposed to discrete molded plastic strain reliefs or seals.
For example, Jenets (U.S. Pat. No. 6,439,929, Aug. 27, 2002) discloses a standard strain relief application: “Often times, these terminating backshells are intended to be filled with a potting compound, such as at non-conductive epoxy or the like, which will protect soldered wire joints from the environment and to prevent corrosion, while at the same time providing some degree of strain relief to soldered wire joints.” Similar disclosure is found in Burger, et al. (U.S. Pat. No. 6,146,196, Nov. 14, 2000): “After termination, the back end of the coaxial contact system would be potted with epoxy to further lock in place and to provide strain relief.”
Takahashi, et al. (U.S. Pat. No. 5,679,008, Oct. 21, 1997) describes a similar strain relief: “It is preferable that the vinyl jackets 54 of the coaxial cables 5 are fixed to the circuit boards 41 with epoxy resin in order to reinforce the attachment of the coaxial cables 5, providing strain relief.”
The prior art is replete with examples of the use of epoxy resins as stabilizing, sealing, and strain relief agents when used in the construction of cable connections. However, not disclosed is the possibility and express intention that the epoxy used in the potting process wicks into the cable along the interfaces between the various members of the cable's structure, cures there, and provides strain relief actually within the structure of the cable itself.
Bryant, et al. (U.S. Pat. No. 7,430,881, Oct. 7, 2008) discloses an optical fiber termination means where epoxy wicks into a tube around a fiber: “ . . . the pigtail 102 may be heated to wick epoxy up through the maria 205. The protective sleeve 203 may then be reinserted and the epoxy allowed to cure (e.g., via UV curing), thus providing strain relief and securing the protective sleeve 203 without interfering in the optical path.” However, there is no disclosure of the epoxy wicking into the structure of the fiber to provide a strain relief, and all strain relief is external to the fiber.
McNeel (U.S. Registration No. H113, published Aug. 5, 1986) discloses an electrical cable termination and sealing method: “A select epoxy resin 84, such as type CN-874 manufactured by Mereco Company infills housing 82, surrounding the ends of the pins and sockets such as 52 and 60 within flanges 72, the laced wire conductors 66 and 68, brace stem 76, and a predetermined length of cable 14. The epoxy resin 84 forms a watertight seal within housing 82 and reacts chemically with cable 14 firmly anchoring it within the housing.” Here there is still no disclosure of epoxy encapsulant wicking into the structure of the cable and forming a strain relief.
Objects and Advantages of the Cable Connection Method
Several objects and advantages of the cable connection method are:                1. Connections to the triaxial cable can be made in a small space, typically two to four diameters of the cable in length.        2. No elaborate clamping or shell arrangement is needed, and the frame for encapsulation of the connection may be inexpensive plastic.        3. Connections to the cable may be easily wired by soldering wires to the exposed conductors of the cable.        4. The entire connection area is potted in epoxy, which then wicks into the cable, creating a strain relief.        5. The assembly method requires no high tolerance machined parts or expert assembly skills, and can be accomplished with inexpensive materials.        6. The completed connection is impervious to moisture and contaminants.        